Multichannel estimation of frequency-dependent Q from VSP data

Harris, Peter; Kerner, C.; White, Robert S.

doi:10.3997/2214-4609.201410426

Cited by 6 publications

(12 citation statements)

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“…Equation 10shows that the desired amplitude ratio (i.e., A z /A 0 ) appears multiplied by a complicated function that depends on the wavelets, the window, and the attenuation coefficient. As Harris et al (1997) noted, the factor exp(␣f ) increases with frequency, and for this reason it is important that the sidelobes of W(f ) have small amplitudes. From the analysis of synthetic data (Pujol and Smithson, 1991;Wilson, 1990) it was found that the computed values of Q may show a spurious dependence on f , which in turn is a function of the type and length of the window used.…”

Section: Methods To Determine Attenuationmentioning

confidence: 97%

Unexpected Values of Qs in the Unconsolidated Sediments of the Mississippi Embayment

Pujol¹,

Pezeshk²,

Zhang³

et al. 2002

Bulletin of the Seismological Society of America

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We studied the attenuation of shear waves at three sites in the Mississippi embayment using data recorded in boreholes drilled to depths of up to 60 m. The source was a highly repeatable compressed-air-driven hammer. To estimate attenuation we used a spectral ratio technique for fixed depth and variable frequency. The best-fit line for each depth z gives a measure of the cumulative attenuation, indicated by ␣(z). Then we fit a straight line to ␣(z) for a range of values of z. The slope of this line gives an estimate of the average attenuation per distance and was used to determine an average Q s. For one of the sites (Newport, northeastern Arkansas), Q s ranges between 34 (1.5 m Յ z Յ 44.2 m) and 44 (1.5 m Յ z Յ 51.8 m). These values are significantly higher than the more typical value of about 10 determined for unconsolidated sediments by other authors. In addition, these high values correspond to sediments with low average shear-wave velocity (about 300 m/sec). In contrast, average Q s and velocity for sediments in Shelby Forest (near Memphis, Tennessee) are 22 and 348 m/sec (22.6 m Յ z Յ 60.1 m), respectively. Therefore, these results go against the conventional wisdom that low velocity implies low Q. For the third site (Marked Tree, northeastern Arkansas), average Q s and velocity are 18 and 251 m/sec (9.8 m Յ z Յ 33.6 m), respectively. This site is about 75 km from Newport, and the differences in attenuation appear related to differences in lithology.

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Section: Methods To Determine Attenuationmentioning

confidence: 97%

Unexpected Values of Qs in the Unconsolidated Sediments of the Mississippi Embayment

Pujol¹,

Pezeshk²,

Zhang³

et al. 2002

Bulletin of the Seismological Society of America

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“…Seismic attenuation (Wang 2009), defined by the parameter β which can depend on the frequency f , can be expressed as where A z and A 0 are the wavefield amplitudes at depth z and at a reference depth z 0 , respectively. Regarding the decrease of the seismic data ridge functions with frequency, we can assume an attenuation coefficient β which depends linearly on the frequency (Hamilton 1972; Harris et al 1997), although several papers suggest a power law between β and f (Best et al 2001 and Wang 2009 for a review). In our case, the attenuation coefficient is β≃ 0.14 d B /λ, corresponding to a quality factor Q ≈ 200 in accordance with the upper part of the Q range (30–180) measured for very fine silt and clay sediments (Shumway 1960; Hamilton 1972; Stevenson et al 2002).…”

Section: Application Of the Wr To Deep‐water Hr And Vhr Seismic Datamentioning

confidence: 99%

Multiscale seismic attributes: a wavelet-based method and its application to high-resolution seismic and ground truth data

Ker

Gonidec

Gibert

et al. 2011

Geophysical Journal International

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International audienceWe propose a wavelet-based method to characterize acoustic impedance discontinuities from a multiscale analysis of seismic reflected waves. Our approach relies on the analysis of ridge functions which contain most of the information of the wavelet transform in a sparse support. This method falls in the framework of the wavelet response (WR) introduced by Le Gonidec et al. which analyses the impedance multiscale behaviour by propagating dilated wavelets into the medium. We further extend the WR by considering its application to broad-band seismic data. We take into account the bandpass filter effect related to the limited frequency range of the seismic source. We apply the method to a deep-water seismic experiment performed in 2008 during the ERIG3D cruise to demonstrate the potential of ridge functions as multiscale seismic attributes. In conjunction to the analysis of seismic data acquired by the deep-towed SYSIF system (200-2200 Hz), we use ground truth data to characterize the fine scale structure of superficial sediments by using the continuous wavelet transform (CWT). The availability of in situ measurements allows to validate the relationship between CWT andWR and to estimate the attenuation of seismic waves into the sediments. Once validated, the method is applied on a whole seismic profile and WR ridge functions are computed for two particular reflectors. The reflector thicknesses fall below the resolution limit of the seismic experiment making the WR seismic attributes a super-resolution method

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“…This is also the conclusion of investigations of different estimation techniques (Tonn, 1991). The evaluation of a frequency dependence is even more uncertain (Harris et al, 1997). A partial explanation for these may be sought in the masking effect of other attenuating phenomena, such as geometric spreading and scattering from irregularities and layering.…”

Section: Discussionmentioning

confidence: 96%

“…There are in fact very few measurements of Q −1 within the seismic frequency band (5-50 Hz) and at hydrocarbon exploration depths. Those that exist are generally the result of VSP analyses (for example, McDonal et al, 1958;Pujol and Smithson, 1991;Tonn, 1991;De et al, 1994;Harris et al, 1997). In these, although there may be agreement with some specific features of the individual lithologies, there is little overall consensus to be drawn.…”

Section: Attenuation and Qmentioning

confidence: 99%

Azimuthal variation inP-wave signatures due to fluid flow

MacBeth

1999

GEOPHYSICS

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The favored dominant mechanism for attenuation in the upper crust at seismic frequencies is intracrack fluid flow. In cracked media, the azimuthal attenuation of the P-wave amplitudes arising from such flow is predicted to be quite substantial. The consequence of this variation in azimuth is a modification in the amplitude behavior of the base event from a cracked reservoir due to transmission through the attenuative layer. Indeed, the effect is of sufficient strength to exacerbate, diminish, or reverse variations that arise solely due to the reflectivity coefficient. Thus, although this attenuation is always greatest perpendicular to the crack strike, the direction of the dimming or brightening of the base reservoir event will depend upon the exact attenuation law and the crack properties. The combination of these factors contributes to a wave behavior that can provide a more adequate discrimination between conditions of brine and oil fill than an interpretation assuming the reflection coefficient alone. Unfortunately, regions of commonality do remain, and the distinction between fills is still only apparent for particular reservoir and crack conditions. The attenuated amplitudes are large enough to be seen at small offsets and may possibly account for the significant azimuthal variations in the P-wave signatures observed in field data.

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Multichannel estimation of frequency-dependent Q from VSP data

Cited by 6 publications

References 0 publications

Unexpected Values of Qs in the Unconsolidated Sediments of the Mississippi Embayment

Unexpected Values of Qs in the Unconsolidated Sediments of the Mississippi Embayment

Multiscale seismic attributes: a wavelet-based method and its application to high-resolution seismic and ground truth data

Azimuthal variation inP-wave signatures due to fluid flow

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